This invention is generally related to switch mode power supplies (SMPS). More particularly, this invention is related to methods and circuits for improving the output characteristics of SMPS. Merely by way of example, the invention has been applied to reduce the output voltage overshoot of a pulse width modulated (PWM) or a pulse frequency modulated (PFM) switching mode power supply. But it would be recognized that the invention has a much broader range of applicability.
Switching mode power supplies (SMPS) have the advantages of smaller size, higher efficiency and larger output power capability, and are widely applied in mobile phone chargers, notebook computer adapters and other fields. In recent years, green power supplies are emphasized, which require higher conversion efficiency and especially lower standby power consumption. However, under certain operating conditions, for example, when the SMPS changes from a heavy load condition to a low load or no load condition, the output can overshoot. This can lead to output instability and power loss.
In view of the foregoing, there is a need for an effective technique to reduce the output voltage overshoot or over-voltage during load transients or dynamic load changes of switching mode power supplies.